Currently Portage is showing its age. The code of Portage does not seem to be
salvageable for new versions. As of the date of publication, there are two known
alternative package managers that claim a level of Portage compatibility. These
alternatives are paludis[1] and pkgcore[2]. Before these alternatives are
developed further, a set of rules should be created to level the playing field
and ensuring that decisions can be made clearly.

We distinguish four categories of package managers. While a package manager can
transition from one category to another, it can not be in two categories at the
same time. It can be in a state of transition though.

Primary Package Manager

There is one primary package manager. Currently this position is held by
Portage. The primary package manager is assigned by the council and all
packages in the official tree must be installable by a usable version of the
primary package manager.

Candidate Primary Package Managers

A candidate Primary Package Manager does aim, or show an aim, at replacing
the current primary package manager. At a point where the package manager is
deemed stable a decision must be made whether this package manager should
become the new primary package manager. At that point the Primary package
manager transition phase starts.

Secondary Package Managers

A secondary package manager is a package manager that coexists with the
primary package manager, while not aiming to replace it. Examples of package
managers that would fall into this category are:

Experimental package managers. Package managers whose purpose it is to try
out new features.

Focused package managers. For example a package manager that allows the
use of RPM formatted binary packages would be an example.

Alternate package managers. Package managers that aim to coexist with the
primary package manager. They might for example offer a nicer user
interface than the primary package manager (e.g. show a cow instead of
compilation messages).

Third Party Package Managers

A third party package manager is any package manager that lacks recognition
from Gentoo as being in any other category. A third party package manager may
or may not have a Gentoo package, but is not supported beyond that.

As a package manager is in a state of higher support there are higher
requirements to it. The purpose of these requirements is to ensure the unity of
the distribution and the package tree. For this purpose it is needed that there
is only one primary package manager. This is from gentoo's perspective. From a
user perspective it is perfectly possible to use another package
manager. Candidate primary package managers and secondary package managers are
also supported in regards to bugs etc.

The primary package manager is the package manager that sets the standards for
the tree. All ebuilds in the tree must function with the primary package
manager. As the primary package manager sets the standard it does not have to
maintain compatibility with other package managers. This does not mean that the
actual implementation is the standard, but that the maintainers have the ability
to define new standards, together with the other involved gentoo projects.

The primary package manager does however have the responsibility that it must be
very stable. The primary package manager must maintain compatibility with old
versions of itself for extended periods of time. This compatibility time is set
by the council. The suggested time would be one year from the point that there
is a compatible stable version for all supported architectures.

Another compatibility requirement for the primary package manager is a limited
forward compatibility. It must always be possible to transition from the
unstable version of the primary package manager to a stable version. This may be
done either by first introducing reading compatibility for a new format and only
having write support later. Another way would be the provision of a conversion
tool that ensures that the on disk information maintained by the package manager
is supported by the stable package manager.

The primary package manager maintainers further have the responsibility to allow
competition. This means that reasonable patches from the maintainers of
secondary or candidate primary package managers must be applied, given that
these patches are as independent of that package manager as possible.

The primary package manager is maintained on official Gentoo infrastructure,
under control of Gentoo developers.

A candidate primary package manager aims to replace the primary package
manager. The council is responsible for deciding whether this is done. The
requirements are there to ensure that it is actually possible to transition a
candidate primary package manager into the primary package manager.

First of all, there must exist a transition path. This means that the on disk
data of the primary package manager can be used by (or converted to a format
usable by) the candidate primary package manager.

Second, there must be a test path. It must be possible for the developers to
test out the candidate primary package manager on their working systems. This
means that the transition path must exist. This also means that there are no
serious obstacles for reverting to the current primary package manager. This
reverting must also be usable when it is decided that the candidate will not
become primary package manager, for example because serious design flaws or bugs
were found. Ideally, the Candidate Primary Package Manager and the Primary
Package Manager can be installed simultaneously. If not, clear instructions must
be provided for both ways of transitioning.

Third, there must exist an ebuild test path. It must be possible for package
managers to test ebuilds in one tree for both the primary as well as the
candidate primary package manager. It is not an issue if this requires a special
mode for the candidate primary package manager. It is not an issue either if
compatibility can be achieved by having the candidate primary package manager
unmerge the package.

Fourth, there must be support. This means that the package manager is actively
maintained under control of Gentoo. If it is not maintained on Gentoo
infrastructure, the means must be there to move the package manager, with its
change history, to Gentoo infrastructure. This means that it must be maintained
on a Gentoo supported versioning system, or on a version system whose history
can be converted to a Gentoo supported versioning system.

Fifth, release capabilities. There must exist automated tools that use the
candidate primary package manager to create release media that have similar
capabilities as those released using the old primary package manager. The exact
requirements are determined by the Release Engineering project, but should not
be significantly beyond what is currently implemented using the primary package
manager.

A secondary package manager is a package manager that instead of directly aiming
at replacing the current primary package manager as primary package manager aims
to cooperate with the primary package manager. As such a secondary package
manager does not set the standard on the tree, but follows the standard set by
the primary package manager.

There are two kinds of secondary package managers. The first kind is formed by
those that do not maintain their own installed package database, but work with
the package database of the primary package manager. While these package
managers can put additional information in the database, these entries must
remain compatible with the primary package managers. Verification, reference,
and deinstallation by the primary package manager must remain functional.

The second kind is formed by those package managers that maintain their own
package database, or a package database incompatible with the primary package
manager. To ensure the secondary role of these package managers the support in
the tree for these package managers is provided along with restrictions.

The first restriction is that no packages in the tree must rely on the secondary
package manager. While packages may provide a level of support (while being
compatible with the primary package manager) this may not result in a
significant increase of features. If this were allowed, this would mean that
while they technically work with the primary package manager, there would be
significant incentive to use the secondary package manager. As the use of this
secondary package manager disallows the parallel use of the primary package
manager, this would result in users using the secondary package manager as their
primary package manager.

Users are allowed to make their own choices. However by making the tree favour a
package manager that is not the primary package manager, this will lead to the
secondary package manager becoming the effective primary package manager. As
this will be a decision by default instead of a conscious choice by the council,
this is an undesirable result.

There is one exclusion for the restriction of packages that only work with or
have significant improvements with the secondary package manager. That is
packages that by their nature are only usable with this secondary package
manager. An example would be a graphical front-end to the secondary package
manager.

If a secondary package manager works along the primary package manager, but by
itself does not have the capabilities of becoming a primary package manager the
risks of choice by default are lower. As a result, the council could choose to
allow the inclusion of packages that work only or significantly better with this
secondary package manager. For example at a point where there is a stable,
functional, package manager that can handle RPM format packages, the council
could decide to include these packages directly in the tree, instead of using
wrapper scripts for those packages that are only provided in the RPM
format. Such a decision does imply that the maintainers of the primary package
manager must take this secondary package manager into account.

A third party package manager is just that. It is a package manager without any
support within Gentoo. As there is no control by Gentoo over the package manager
this means that there are no requirements on the package manager.

This complete lack of control however also translates to the fact that Gentoo
can not make package manager specific changes to support this package
manager. Package manager specific means that it is possible to request changes
that make the tree more independent of the primary package manager. These
changes must however be agnostic of the package manager, and only make it easier
to have alternative package managers.

A candidate primary package manager can be chosen to become primary package
manager. This can only happen by council decision. This decision can only be
made when the candidate primary package manager is stable on all stable
architectures. (all architectures except experimental ones). There is a
incubation period of at least 3 months before a candidate primary package
manager can become the primary package manager.

After the decision has been made to replace the primary package manager, the
transition phase starts. The use of the old stable package manager must remain
supported for a period of 6 months. This means that core packages must be
installable by this package manager. Further the possibility to convert the
system automatically to the new primary package manager must be available for at
least 18 months, but preferably longer (enable installing the new package
manager from the old one).

During the transition phase packages are allowed in the tree that use the new
features of the new primary package manager. While backward compatibility with
the previous primary package manager must be maintained a forward compatibility
is no longer needed.

The transition from secondary package manager to candidate primary package
manager is straightforward. The secondary package manager must satisfy all
requirements for a candidate primary package manager. At that point its
maintainers can announce that they are changing the status to candidate primary
package manager. This allows a greater support from Gentoo in achieving that
goal.